The present invention relates to a method of producing cyanopyridines by means of the catalytic reaction of methylpyridines with ammonia and oxygen at elevated temperature. The present invention also relates to catalysts suitable for this purpose which contain compounds of the elements antimony, vanadium, silicon, titanium and oxygen and compounds of one or more of the alkali metals. Furthermore, the present invention relates to the method of producing the catalysts and method of their use.
Several methods of producing cyanopyridines by reacting the appropriate methylpyridines with oxygen and ammonia at elevated temperature in the gaseous phase are known. They differ from each other by the reaction conditions and especially by the catalyst composition. Of the known methods and catalysts, the significant ones are those for use on an industrial scale which have a good selectivity and dwell time and which at the same time have a high space-time yield.
It is furthermore known that catalysts can be used which are produced by pretreating mixtures containing antimony and vanadium in an atomic ratio of 1.1:1 to 50:1 and at least one of the elements iron, copper, titanium, cobalt, manganese and nickel and optionally a carrier substance by heating to temperatures of 600.degree. to 1100.degree. C. in the presence of oxygen (U.S. Pat. No. 3,927,007 which is incorporated by reference in its entirety, especially for its teaching of compounds of Sb, V and Ti which can be used to form a catalyst; DE 20 39 497). This method achieves high space-time yields but the selectivity is unsatisfactory.
It is also known that catalysts for the ammonoxidation of methylpyridines based on titanium oxide/silicon oxide carriers can be produced which are covered with the oxides of antimony and of vanadium (U.S. Pat. No. 4,939,260 which is incorporated by reference in its entirety; EP 0,290,996 B1). These catalysts have yields of only around 85% in the case of the ammonoxidation of 3-methylpyridine.
It is furthermore known that catalysts for the production of 3-cyanopyridine with good selectivity and high space-time yield can be produced from layer-lattice silicates, highly dispersed silicon oxide and oxygen compounds of the elements antimony and vanadium and from at least one of the elements iron, copper, titanium, cobalt, manganese and nickel (EP 0,059,414 B1; U.S. Pat. No. 4,447,612 which is incorporated by reference in its entirety). The production of these catalysts is very expensive and requires, among other things, an intermediate calcining with subsequent grinding.